Remove Collection, Collections and clean up List/Set/Queue implementations of retain/remove.

samples/swarm/DataSource.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of swarmlib;
 
 /** The top-level collection of all sections for a user. */
 // TODO(jimhug): This is known as UserData in the server model.
-class Sections extends Collection<Section> {
+class Sections extends Iterable<Section> {
   final List<Section> _sections;
 
   Sections(this._sections);
 
   operator [](int i) => _sections[i];
 
   int get length => _sections.length;
 
   List<String> get sectionTitles =>
     _sections.map((s) => s.title).toList();
@@ skipping 211 matching lines @@
     final hasThumbnail = decoder.readBool();
     final author = decoder.readString();
     final dateInSeconds = decoder.readInt();
     final snippet = decoder.readString();
     final date =
         new DateTime.fromMillisecondsSinceEpoch(dateInSeconds*1000, isUtc: true);
     return new Article(source, id, date, title, author, srcUrl, hasThumbnail,
         snippet);
   }
 }